The invention relates to a reflection mirror for an vehicle lamp that allows rays of reflecting light to be utilized as controlled rays of light for formation of luminous intensity distribution, the rays of reflecting light being reflected at an inner surface of a circumferential wall portion arranged around a main reflection portion that includes a region close to an intersecting point between a main optical axis of the reflection mirror and the reflection mirror.
A vehicle lamp basically includes: a lamp body having an opening at one end thereof; a reflection mirror arranged within the lamp body or a reflection portion formed by subjecting a part of the lamp body to a reflection treatment; and an outer lens that covers the opening of the lamp body. The reflection surface of the reflection mirror or the reflection portion is formed into, e.g., a paraboloid of revolution that is symmetric about the optical axis of the lamp.
Lamps whose front is circular or square are known. In this case, the circumferential wall portion that surrounds a main reflection portion including a region close to an intersecting point between the main optical axis of the reflection mirror or the reflection portion and the reflection mirror or the reflection portion, is formed to be flat. Therefore, rays of light reflected at the circumferential wall portion out of rays of light emitted from a light source located between the outer lens and the reflection mirror or the reflection portion within the lamp become ineffective for luminous intensity distribution, which in turn hampers improvement in efficiently utilizing luminous fluxes.
In order to overcome this problem, various types of lamps have been developed, such lamps being characterized by forming irregular reflection surfaces or the like on the circumferential wall portion. For example, U.S. Pat. No. 4,979,077, U.S. Pat. No. 4,794,504, and the like disclose such lamps.
The reflection mirror for the aforementioned lamps utilizes rays of irregularly reflected light or diffused light at the circumferential wall portion. These rays of light are, in the end, not rays of reflecting light that are so well controlled as to be oriented toward a predetermined direction. As a result, there is a limitation in utilizing such rays of light as effective rays of light for luminous intensity distribution for the lamp.
To overcome this problem, it is conceivable either to reduce the area of the inner surface of the circumferential wall portion by forming the reflection surface of the reflection mirror or the reflection portion of a plurality of regions, e.g., a combination of paraboloids of revolution whose focal distances are different from one another, or to control rays of light heading toward the circumferential wall portion from a light source by interposing an inner lens between the outer lens of the lamp and the reflection mirror or the reflection portion. However, a significant uneven portion may be formed at the borders between the surfaces constituting the reflection surface in the former case, whereas the inner lens increases the cost of manufacture in the latter case.